Passive carrier-based device delivery for slot-based high-volume semiconductor test system

ABSTRACT

A testing apparatus comprises a tester comprising a plurality of racks, wherein each rack comprises a plurality of slots, wherein each slot comprises: (a) an interface board affixed in a slot of a rack, wherein the interface board comprises test circuitry and a plurality of sockets, each socket operable to receive a device under test (DUT); and (b) a carrier comprising an array of DUTs, wherein the carrier is operable to displace into the slot of the rack, and wherein each DUT in the array of DUTs aligns with a respective socket of the plurality of sockets on the interface board. The testing apparatus further comprises a pick-and-place mechanism for loading the array of DUTs into the carrier and an elevator for transporting the carrier to the slot of the rack.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application also claims priority to U.S. Provisional Application63/108,792 titled “Passive Carrier-Based Device Delivery For Slot-BasedHigh-Volume Semiconductor Test System,” filed on Nov. 2, 2020. Theentire contents of the above-listed application is hereby incorporatedby reference for all purposes as if fully set forth herein.

FIELD OF THE INVENTION

The present disclosure relates generally to the field of automated testequipment and more specifically to techniques for massively parallelhigh-volume testing of devices under test.

BACKGROUND OF THE INVENTION

Automated test equipment (ATE) includes any testing assembly thatperforms a test on a semiconductor wafer or die, an integrated circuit(IC), a circuit board, or a packaged device such as a solid-state drive.ATE assemblies may be used to execute automated tests that quicklyperform measurements and generate test results that can then beanalyzed. An ATE assembly may be anything from a computer system coupledto a meter, to a complicated automated test assembly that may include acustom, dedicated computer control system and many different testinstruments that are capable of automatically testing electronics partsand/or semiconductor wafer testing, such as system-on-chip (SOC) testingor integrated circuit testing. ATE systems both reduce the amount oftime spent on testing devices to ensure that the device functions asdesigned and serve as a diagnostic tool to determine the presence offaulty components within a given device before it reaches the consumer.ATE systems can also be used to test and record device performance forpass/fail and for device binning determinations.

When a typical ATE system tests a device (commonly referred to as adevice under test or DUT), the ATE system applies stimuli (e.g.electrical signals) to the device and checks responses (e.g., currentsand voltages) of the device. Typically, the end result of a test iseither “pass” if the device successfully provides certain expectedresponses within pre-established tolerances, or “fail” if the devicedoes not provide the expected responses within the pre-establishedtolerances. More sophisticated ATE systems are capable of evaluating afailed device to potentially determine one or more causes of thefailure. Other ATE systems can categorize a performance of a device forbinning purposes.

There are several different types of ATE systems currently existing inthe marketplace. One of them involves transporting devices under test(DUTs) on Tester Interface Boards (TIBs) that include sockets and activetest circuitry. The advantage of transporting DUTs using TIBs is that aseparate apparatus for device transport is not required. The TIB is usedfor both testing and transport. Further, the alignment of the DUTs canbe performed at a central alignment station. This is particularly usefulwhere vision alignment for finer pitches is required. Also, blind-mateconnectors for TIBs allow quick replacement for servicing. ATE systemsusing TIBs have several drawbacks. For example, the high-frequencysignal path between the socket (per DUT) test circuitry and theequipment in a test rack is repeatedly disconnected during normal testoperation, making maintenance of signal fidelity and high-speed signalpath calibration difficult. Further, there is an increased cost (both aninitial set-up cost and maintenance costs) for high cycle counthigh-frequency connectors between a TIB and a test rack.

Another type of ATE system involves inserting DUTs directly into socketson stationary test boards with pick-and-place assemblies. In thissolution, a single centralized pick-and-place assembly is used totransfer the DUTs between JEDEC trays and test sockets on fixed-locationtest boards. This type of ATE system has its advantages also. Forexample, this type of ATE system does not require additional mechanicalcomponents other than the pick-and-place assembly. Further, shieldingand other top-side contact solutions are easy to implement due toavailable space. Nevertheless, this type of ATE systems also has itsdrawbacks. For example, parallelism and Units Per Hour (UPH) (unitstested per hour) is severely limited so this type of ATE system isunsuitable for high-volume manufacturing (HV) applications. Further,there is a low utilization of the expensive pick-and-place apparatus,which often sits idle when the test time is long.

A different type of ATE system transports DUTs to test slots (orstations) on JEDEC trays and loads them into test slots with per-slotpick-and-place assemblies. In this solution, each test slot or stationhas its own dedicated pick-and-place assembly which transfers the DUTsbetween the JEDEC trays or carriers and fixed-location test boards. Thetrays are transported between a central loading/unloading station andthe test slots using a mechanical robotic system that can be implementedwith elevators/conveyors or a robotic arm. Again, there are drawbacksassociated with this type of system. For example, the per-slot pick andplace assemblies increase system cost. Further, there is a lowutilization of per-slot pick-and-place assemblies, which often sit idlewhen test time is long. These types of ATE systems may also potentiallybe unreliable due to multiple pick-and-place assemblies.

Finally, the classic memory tester and handle type of conventional ATEsystem also has many associated drawbacks. In this solution, the handleruses a pick-and-place mechanism to load DUTs from JEDEC trays intomulti-DUT carriers that are moved to the testing chamber. The DUTsremain in the carrier while being simultaneously plunged into socketswhich provide the electrical connection with the test equipment in thetest system. The disadvantage with this system is that memory testersand handlers specifically work only with memory and do not incorporateshields for radio frequency (“RF”) or any type of top-side contact.Further, space requirements for System Level Test (SLT) test circuitryand lack of any vertically-stacked slot architecture limit parallelism.

BRIEF SUMMARY OF THE INVENTION

Accordingly, there is a need for an ATE system that addresses thedrawbacks associated with conventional ATE tester systems. Embodimentsof the present invention provide a massively parallel high-volume testcapability in a slot-based architecture, using multi-device passivecarriers to transport the semiconductor devices from theloading/unloading station to the test slots. This eliminates therequirement to move the test sockets and/or test circuitry with thedevices, which is the method used in the current state-of-the-arthigh-volume slot-based test systems. Eliminating this requirementsimplifies the design of the system and provides improved performance(especially for RF and other high frequency applications), improvedreliability, and reduced cost.

In one embodiment, the slot-based tester system comprises: a) a tester(including power delivery board and controls); b) a tester board such asATE load-board, or Test Interface Board (TIB) comprising a plurality ofSocket Interface Boards (SIB), or Burn-In Board (BIB) comprising aplurality of DUT Interface boards (DIB); c) an open socket to hold oneor more DUTs (Device Under Test); d) a passive carrier/test tray thatholds multiple DUTs (note that multiple carriers or test trays may bepresent in the system); e) an optional parallel cover assembly system(PCA) to place socket covers (or optional RF shields) on top of DUTs inthe carrier; f) a handler and movement system similar to a memory testhandler that places DUTs into carriers and further places the DUTswithin the carriers on top of the sockets; and g) plungers to push downthe socket covers (and/or the optional RF shields) and DUTs into thesockets.

In one embodiment, a testing apparatus is disclosed. The testingapparatus comprises a tester comprising a plurality of tester racks,wherein each tester rack comprises a plurality of slots, wherein eachslot comprises: (a) an interface board affixed in a slot of a testerrack, wherein the interface board comprises test circuitry and aplurality of sockets, each socket operable to receive a device undertest (DUT) and (b) a carrier comprising an array of DUTs, wherein thecarrier is operable to displace into the slot of the tester rack, andwherein each DUT in the array of DUTs aligns with a respective socket ofthe plurality of sockets on the interface board. The testing apparatusfurther comprises a pick-and-place mechanism for loading the array ofDUTs into the carrier and an elevator for transporting the carrier tothe slot of the tester rack.

In one embodiment, a method of testing DUTs is disclosed. The methodcomprises disposing an array of DUTs on a carrier using a handler andtransport system and transporting the carrier to a slot of a rackassociated with a tester using an elevator, wherein the tester comprisesa plurality of racks, wherein each rack of the plurality of rackscomprises a plurality of slots. Further, the method comprises insertingthe carrier into the slot of the rack and affixing an interface board inthe slot of the rack, wherein the interface board comprises a pluralityof sockets, and wherein each socket of the plurality of sockets isoperable to receive a respective device under test (DUT), and whereineach DUT in the array of DUTs aligns with a respective socket of theplurality of sockets on the interface board. The method also comprisesactuating a socket cover of a plurality of socket covers onto each DUTin the array of DUTs to push the respective DUT to make physical andelectrical contact with a respective socket of the plurality of sockets.

In one embodiment, a testing system is disclosed. The system comprises astation operable to load and unload devices under test (DUTs) from aplurality of carriers, wherein the station comprises a pick-and-placemechanism and a trolley operable to transport the plurality of carriersbetween the station and at least one tester. The at least one testercomprises a plurality of racks, wherein each rack comprises a pluralityof slots, wherein each slot comprises: (a) an interface board affixed ina slot of a rack, wherein the interface board comprises test circuitryand a plurality of sockets, each socket operable to receive a deviceunder test (DUT); (b) a carrier comprising an array of DUTs, wherein thecarrier is operable to position into the slot of the rack, and whereineach DUT in the array of DUTs aligns with a respective socket of theplurality of sockets on the interface board. The system furthercomprises an elevator for transporting the carrier to the slot of therack from the trolley.

Using the beneficial aspects of the systems described, without theirrespective limitations, embodiments of the present invention provide anovel solution to address the drawbacks mentioned above.

The following detailed description together with the accompanyingdrawings will provide a better understanding of the nature andadvantages of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example,and not by way of limitation, in the figures of the accompanyingdrawings and in which like reference numerals refer to similar elements.

FIG. 1 illustrates a perspective view of a tester system that combines acarrier-based DUT delivery mechanism with a slot-based test architecturein accordance with embodiments of the present invention.

FIG. 2A is an illustration of a TIB placed in a slot of a conventionaltester.

FIG. 2B is an illustration of a TIB that remains fixed in a slot of atester rack while a passive carrier tray (as discussed above) slidesinto the slot to move DUTs into the tester rack in accordance withembodiments of the present invention.

FIG. 2C provides a top view of the manner in which a carrier slides intoa slot in accordance with an embodiment of the present invention.

FIG. 3A illustrates a side-view of a conventional tester 302.

FIG. 3B illustrates a side-view of a tester that allows the TIB toremain fixed in the slot while the carriers are moved in and out of theslot in accordance with embodiments of the present invention.

FIG. 4 illustrates an alternate slot-based system where trolleys areused to transport the TIBs, BIBs, or carriers between the pick and placehandler and the tester racks in accordance with embodiments of thepresent invention.

FIG. 5 illustrates the manner in which the socket, the carrier, and thesocket cover combine to form the per-DUT shielding in accordance withembodiments of the present invention.

FIG. 6 illustrates a single site exploded view of a DUT in a carrierwhere socket grippers are used for local force cancellation inaccordance with embodiments of the present invention.

FIG. 7 depicts a flowchart of an exemplary process of testing DUTsaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to embodiments, examples of whichare illustrated in the accompanying drawings. While the embodiments willbe described in conjunction with the drawings, it will be understoodthat they are not intended to limit the embodiments. On the contrary,the embodiments are intended to cover alternatives, modifications andequivalents. Furthermore, in the following detailed description,numerous specific details are set forth in order to provide a thoroughunderstanding. However, it will be recognized by one of ordinary skillin the art that the embodiments may be practiced without these specificdetails. In other instances, well-known methods, procedures, components,and circuits have not been described in detail as not to unnecessarilyobscure aspects of the embodiments.

Notation and Nomenclature Section

Some regions of the detailed descriptions (e.g., FIG. 7 ) which followare presented in terms of procedures, logic blocks, processing and othersymbolic representations of operations on data bits within a computermemory. These descriptions and representations are the means used bythose skilled in the data processing arts to most effectively convey thesubstance of their work to others skilled in the art. In the presentapplication, a procedure, logic block, process, or the like, isconceived to be a self-consistent sequence of steps or instructionsleading to a desired result. The steps are those requiring physicalmanipulations of physical quantities. Usually, although not necessarily,these quantities take the form of electrical or magnetic signals capableof being stored, transferred, combined, compared, and otherwisemanipulated in a computer system.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the present invention,discussions utilizing the terms such as “testing,” “affixing,”“coupling,” “inserting,” “actuating,” or the like, refer to the actionand processes of a computer system, or similar electronic computingdevice, that manipulates and transforms data represented as physical(electronic) quantities within the computer system's registers andmemories into other data similarly represented as physical quantitieswithin the computer system memories or registers or other suchinformation storage, transmission or display devices.

The description below provides a discussion of computers and otherdevices that may include one or more modules. As used herein, the term“module” or “block” may be understood to refer to software, firmware,hardware, and/or various combinations thereof. It is noted that theblocks and modules are exemplary. The blocks or modules may be combined,integrated, separated, and/or duplicated to support variousapplications. Also, a function described herein as being performed at aparticular module or block may be performed at one or more other modulesor blocks and/or by one or more other devices instead of or in additionto the function performed at the described particular module or block.Further, the modules or blocks may be implemented across multipledevices and/or other components local or remote to one another.Additionally, the modules or blocks may be moved from one device andadded to another device, and/or may be included in both devices. Anysoftware implementations of the present invention may be tangiblyembodied in one or more storage media, such as, for example, a memorydevice, a floppy disk, a compact disc (CD), a digital versatile disc(DVD), or other devices that may store computer code.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to limit the scope of the presentinvention. As used throughout this disclosure, the singular forms “a,”“an,” and “the” include plural reference unless the context clearlydictates otherwise. Thus, for example, a reference to “a module”includes a plurality of such modules, as well as a single module, andequivalents thereof known to those skilled in the art.

Passive Carrier-Based Device Delivery for Slot-Based High-VolumeSemiconductor Test System

As noted above, there are several different types of ATE systemscurrently existing in the marketplace, each with their own set ofstrengths and weaknesses. In many systems, the high-frequency signalpath between the socket test circuitry and the test equipment in thetest rack is repeatedly disconnected during normal test operation,making maintenance of signal fidelity and high-speed signal pathcalibration difficult. Other types of ATE systems are unsuitable forhigh-volume manufacturing applications because the parallelism in theseATE systems is severely limited. In yet other ATE systems, lowutilization of the expensive components of the test system, e.g., thepick-and-place assemblies is problematic.

Embodiments of the present invention address the drawbacks ofconventional ATE systems by providing a massively parallel high-volumetest capability in a slot-based architecture, using multi-device passivecarriers to transport the semiconductor devices from theloading/unloading station to the test slots. This eliminates therequirement to move the test sockets and/or test circuitry with thedevices. Eliminating this requirement simplifies the design of thesystem and provides improved performance (especially for RF and otherhigh frequency applications), improved reliability, and reduced cost.

In accordance with embodiments of the present invention, a slot-basedtester system comprises: a) a tester (including power delivery board andcontrols); b) a tester board such as ATE load-board, or Test InterfaceBoard (TIB) comprising a plurality of Socket Interface Boards (SIB), orBurn-In Board (BIB) comprising a plurality of DUT Interface boards(DIB); c) an open socket to hold one or more DUTs (Device Under Test);d) a passive carrier/test tray that holds multiple DUTs (note thatmultiple carriers or test trays may be present in the system); e) anoptional parallel cover assembly system (PCA) to place socket covers (oroptional RF shields) on top of DUTs in the carrier; f) a handler andmovement system similar to a memory test handler that places DUTs intocarriers and further places the DUTs within the carriers on top of thesockets; and g) plungers to push down the socket covers (and/or theoptional RF shields) and DUTs into the sockets.

The typical users of the tester system disclosed herein would be:Integrated Device Manufacturers, Fabless Semiconductor Manufacturers,and Outsourced Semiconductor Assembly and Test companies engaged in thehigh-volume manufacturing and test of devices that operate in frequencyranges requiring careful maintenance of signal fidelity between testequipment and DUTs and electrical shielding to reduce interferencebetween individual DUTs during testing. An example DUT would be an RFmodule used in a mobile phone for communications with a cell tower.Embodiments of the present invention are integral to handling andinterfacing solutions included as part of an ATE (Automated TestEquipment) or SLT (System-level Test) system.

Embodiments of the present invention combine a carrier-based DUTdelivery mechanism with a slot-based high volume semiconductor testsystem architecture. FIG. 1 illustrates a perspective view of a testersystem that combines a carrier-based DUT delivery mechanism with aslot-based test architecture in accordance with embodiments of thepresent invention. The tester system comprises a chamber 104 withmultiple racks (e.g., a left and a right rack) with a plurality of slots(e.g., slot 102 in the right rack and slot 103 in the left rack) thatcan be stacked vertically. Stacking the slots vertically allows moreDUTs to be tested in parallel. For example, the chamber 104 can compriseupwards of 30 slots. In a different embodiment, the slots within thetester may be arranged horizontally rather than vertically.

As mentioned previously, the tester system combines the carrier-baseddevice delivery mechanism with the slot-based architecture. The testersystem comprises a pick-and-place mechanism (e.g., incorporated withinhandler 128) that loads the carrier(s) 106 and also further comprises anelevator system 114 that moves the carrier vertically to a particulardesired spot. The advantage of] using the passive carrier or test trayis that all the test electronic circuitry can remain in place in thetest rack while the carrier can be moved into and out of the testerslot. As a result, the TIBs and/or SIBs advantageously do not need to bedisconnected from the tester system. This has advantages for high-speedapplications where the tester needs to maintain a stable and highaccuracy signal path.

Conventional tester systems by comparison had to connect and disconnecttest electronics with the sockets any time new DUTs had to be insertedinto the test racks. This would not be ideal for high speed signal pathswhich require robust connectivity, repeatability and accuracy ofsignals. Embodiments of the present invention advantageously leave thetest circuitry in place during testing. This has advantages for highspeed signal paths and provides reliable connectivity, repeatability andaccuracy of signals.

The high-parallelism architecture provided by embodiments of the presentinvention is advantageous because the test sockets and test circuitryremain in place in a fixed location with continuous connections to testinstrumentation and supporting resources during normal test operations.An example application is an RF or other high-frequency test. In orderto maintain signal fidelity over repeated insertions of the DUTs, theTIBs (Tester Interface Boards) with the sockets and correspondingper-DUT test circuitry remain fixed in the test rack of the system, andare only removed and disconnected for servicing. Since high-frequencytesting requires specialized and costly instrumentation, it is nottechnically or financially feasible to build this equipment into theTIB, so the high-frequency signals pass through connectors between theTIB and the test equipment in the test rack. Accordingly, it isimportant that the connectors not be displaced each time a new set ofDUTs need to be tested.

In conventional high-parallelism SLT systems, the TIBs moveback-and-forth between the pick-and-place assembly for loading/unloadingof the DUTs and the test rack for testing, requiring repeateddisconnecting/reconnecting of the signal paths between the test rack andthe DUTs. In other words, the TIB would need to be regularlydisconnected and pulled out of the slots in order to load new batches ofDUTs.

In the tester assembly of the present invention, the TIB advantageouslydoes not need to be removed in and out of the slot. It remains in placeconnected and does not need to be disconnected to load a fresh batch ofDUTs. With the TIBs remaining fixed in the test rack in accordance withembodiments of the present invention, the tester system uses a passivecarrier or test tray 106 (shown in FIG. 1A) to move the DUTs between thepick-and-place assembly and the test rack. This maintainshigh-parallelism and high UPH (units per hour) without requiringrepeated disconnects of the signal paths. During testing, the entirepassive carrier 106 with multiple DUTs is inserted into a slot in thetest rack, and lowered onto the fixed TIB. The DUTs remain in thecarrier while per-DUT socket covers in the test rack are applied toprovide the necessary force between the DUT and socket to complete theelectrical connections. It should be noted that fixing the TIBs in therack also provides additional flexibility to add external equipment andwire into the test rack.

In one embodiment, the socket covers may be part of a parallel socketcover assembly system that places socket covers on all the DUTs in thecarrier before a plunger is used to actuate the DUTs. Actuating the DUTsmeans to apply contact force on top of the DUTs to push them down tomake electrical contact with the socket electronics. In other words, thesocket covers are placed on the DUTs by the parallel cover assemblysystem. The parallel cover assembly system may be similar to the onedescribed in U.S. patent application Ser. No. 16/986,037, entitled,“Integrated Test Cell Using Active Thermal Interposer (ATI) withParallel Socket Actuation,” filed in Aug. 5, 2020, which is herebyincorporated by reference in its entirety for all purposes. In adifferent embodiment, however, where no parallel cover assembly systemis used, a plunger with a built-in socket cover may be used to push downon the DUTs in the carrier to make contact with the respective sockets.

Embodiments of the present invention eliminate the key disadvantages ofthe conventional tester systems. The high-parallelism architecture ofexisting HVM (High-Volume Manufacturing) SLT systems is adapted forhigh-frequency test applications by incorporating the necessary testequipment, shielding, and high-speed signal paths (cabling, connectors,board traces, etc.). In order to maintain signal fidelity over repeatedinsertions, the TIBs (Tester Interface Boards) with the sockets andcorresponding per-DUT test circuitry remain fixed in the test rack ofthe system, and are only removed and disconnected for servicing.

With the TIBs remaining fixed in the test rack, embodiments of thepresent invention use a passive carrier 106 (as shown in FIG. 1A) ortest tray to move the DUTs between the pick-and-place assembly and thetest rack (or test chamber 104). This maintains a high-parallelism andhigh UPH (units per hour) without requiring repeated disconnects of thehigh-frequency signal paths.

In an embodiment, during testing, the entire carrier with multiple DUTsis inserted into a slot in the test rack, and lowered onto the fixedTIB. The DUTs remain in the carrier while per-DUT socket covers in thetest rack are applied to provide the necessary force between the DUT andsocket to complete the electrical connections. In one embodiment, thesocket covers are typically aligned with pogo pins on top of the deviceor socket to enable the socket covers to form an RF shield incollaboration with the carrier and the socket. As noted above, aparallel cover assembly system may be used to place the socket coversonto the DUTs. In a different embodiment, however, a plunger that has anintegrated socket cover may be used to push down on each DUT in thecarrier to make contact with the respective socket.

In one embodiment, the DUTs on the carrier tray 106 may be spaced fairlyclose to each other and need to be shielded, e.g., in the case of RFDUTs. Because of the proximity between the DUTs, there is a highpotential of cross-talk between devices. Plus, there is less space to beable to introduce the shielding on a per-socket basis. In oneembodiment, therefore, because the carrier stays in place, the carrierstructure itself is incorporated into the shielding as well. Forhigh-frequency applications, the socket covers, together with thesocket, typically provide the required electrical shielding betweenDUTs, as well as providing the means for top-side contact as required.In the proposed implementation, since the DUTs remain in the carrierduring testing, the carrier needs to be an integral part of theshielding design. To address this issue, a novel “sandwich” approach isused where the socket, carrier, and socket cover combine to form theper-DUT shielding.

FIG. 2A is an illustration of a TIB placed in a slot 200 of aconventional tester. As shown in FIG. 2A, the TIB 202 in conventionaltesters is configured to slide in and out of the slot each time a newbatch of DUTs needs to be loaded. The RF board 212 may be affixed to theSIB 213 which is affixed to the TIB 202. In a conventional tester theentire TIB 202 and all the attached components may need to bedisconnected from the tester. The TIB slides out of the slot, new DUTsare loaded and the TIB then slides back into the slot with the new DUTsfor further testing. A blind mate adaptor 274 connects the TIB to thetester rack. As shown in FIG. 2A, the entire TIB 202 with the attachedRF board 212 slides out and then slides back in with a new batch of DUTsand makes contact with the blind mate adaptor 274 to connect the TIB tothe tester rack.

FIG. 2B is an illustration of a TIB that remains fixed in a slot 206 ofa tester rack while a passive carrier tray 204 (as discussed above)slides into the slot to move DUTs into the tester rack in accordancewith embodiments of the present invention. The carrier tray slides in ontop of the socket 205 and the socket cover 209 is lowered, using aplunger (not shown) for example, to push the DUT 281 down into thesocket to make contact. Note that while FIG. 2B only shows a singlesocket, the passive carrier is capable of carrying an array of DUTs thatare aligned with and lowered onto an array of sockets. Similarly, asocket actuator array can comprise an array of socket covers (e.g.,socket cover 209) that correspond to the array of DUTs and the array ofsockets on the TIB. In one embodiment, a parallel cover assembly systemmay be used to position the socket covers onto the DUTs before thesocket actuator array pushes the socket covers onto the DUTs. In adifferent embodiment, the socket actuator array may comprise plungerswith integrated socket covers that are used to actuate the DUTs.

In one embodiment, the carrier tray 204 is sandwiched between the socketcovers and the TIB comprising the sockets. The socket covers (which maybe part of an actuator array) pushes the DUTs down into the sockets. TheDUTs on the carrier are situated in respective pockets of the carrier ona thin membrane. The DUTs rest on the membrane and get pushed into thesocket. The bottom of the DUTs comprises a ball-grid array where thesolder balls of the ball-grid array get pushed through the membrane tomake contact with the socket. In one embodiment, the socket covers willtypically be aligned with pogo pins 282 on top of the device or socketto enable a socket cover 209 in the socket cover array to form an RFshield in collaboration with the carrier 204 and the respective socket205. After the DUTs are done testing, the actuator array rises back upand the carrier slides back out of the slot with the DUTs on it. In thetester therefore, all the TIBs are able to remain in the slot while thecarriers are moved in and out of the various slots during testing.

As mentioned above, socket covers (e.g., socket cover 209) in the testrack are applied to provide the necessary force between the DUT andsocket to complete the electrical connections. For high-frequencyapplications, these covers 209, together with the socket 205 and thecarrier 204, typically provide the required electrical shielding betweenDUTs, as well as providing the means for top-side contact as required.Embodiments of the present invention sandwich the carrier 204 betweenthe socket cover 209 and the socket 205 to provide per-DUT shielding.The socket cover 209, the carrier 204 and the socket 205 together createthe RF shield. Note that each carrier (e.g., carrier 204) comprises anarray of DUTs on it (e.g., an x-y matrix of DUTs). The carrier is pushedonto a TIB 284 that has the sockets (e.g., socket 205) on it. There isalso an array of socket covers (e.g., socket cover 209) above thecarrier that are pushed onto the carrier and the sockets so that thesocket cover, the carrier and the socket together form an RF shield.Each combination of a socket, the carrier and a socket cover creates aseparate RF shield that isolates the respective enclosed DUT from otherDUTs on the carrier.

FIG. 2C provides a top view of the manner in which a carrier slides intoa slot in accordance with an embodiment of the present invention. Asshown in FIG. 2C, the DUT carrier 291 comprises an array of DUTs 296.The DUT carrier 291 slides into the slot so that the DUTs on the carriertray are aligned with the sockets disposed on TIB 292. The actuatorarray 293 is then used to actuate the DUTs onto the sockets as discussedabove.

FIG. 3A illustrates a side-view of a conventional tester 302. As shownin FIG. 3A, in the conventional testers, the elevator 307 moves the TIBsvertically and slides the TIBs 308 (along with the socket and testcircuitry) into the test slots in the tester rack 309. Conventionaltesters move the TIBs between the pick and place assembly and theelevator and, finally, the test rack (with the slots). In conventionaltesters, such as the one shown in FIG. 3A, the TIB needs to be regularlyremoved in and out of the slot, which is problematic for reasonsexplained above.

FIG. 3B illustrates a side-view of a tester 303 that allows the TIB toremain fixed in the slot while the carriers are moved in and out of theslot in accordance with embodiments of the present invention. In oneembodiment, a carrier 325 comprising the DUTs is vertically displaced byelevator 317 and slid into a slot in the tester rack 335. The TIB 326and the power distribution board (PDB) stay in place within the rack335. A plunger 345 can push the DUTs on the carrier into the sockets.The passive carrier 325 is typically the moving component that moves inand out of the rack 335 while the remaining components, e.g., the TIB,PDB and plunger stay within the rack. In one embodiment, multiplecarriers are employed in a tester system to transport DUTs in an out ofthe vertical slots of the tester rack associated with the tester 303.

In one embodiment, dual elevators (or “dual-slot elevators”) are used,e.g., elevator 114 in FIG. 1 or elevator 317 in FIG. 3B may be dual-slotelevators. A dual-slot elevator has two slots arranged vertically, e.g.,slots 327 and 328 in FIG. 3B. One elevator slot is used to bring thecarrier with DUTs from the pick-and-place (PnP) to the test slot. Butsince there is usually already a pre-existing carrier in the test slotthat needs to be removed after testing, the other elevator slot is usedto remove that carrier from the test slot before inserting the newcarrier from the PnP. Once the operation is complete, it takes thetested carrier that it just removed back to the PnP for unloading andloading. This eliminates any need of the elevator assembly having tomake two trips back and forth.

In one embodiment, the dual-slot elevator operates as follows: a)transport a carrier with untested DUTs from the loader/unloader to thetest slot, using one of the two elevator slots; b) remove the carrierwith tested DUTs from the test slot, by loading it into the other(empty) elevator slot; c) move vertically to line up the carrier withuntested DUTs with the same test slot the carrier with tested DUTs wasjust unloaded from, and load the carrier with untested DUTs into thattest slot; and d) transport the carrier with tested DUTs back to theloader/unloader.

In one embodiment, buffer carriers present in the system allowpipelining of multiple carriers. Buffer carriers are additional carriersthat can be loaded with DUTs even when all test slots are filled withcarriers whose DUTs are currently being tested. For example, slots 327and 328 may, in one embodiment, be also able to transport buffercarriers. Using buffer carriers speeds up overall system throughput, asthe loaded buffer carriers are queued up for immediate swapping intotest slots as soon as the previous test cycle has completed. Without thebuffer carriers, test slots would be idle while the carrier is cycledback to the PnP for unloading/loading, then back to the test slot. Notethat this is different than buffer TIBs or burn in boards or load boardswhich actually have expensive sockets and circuitry and hence involve acareful tradeoff of buffer TIB costs v/s UPH improvements. In this case,buffer carriers are purely mechanical and do not involve socket cost andhence as many buffer carriers as needed can be added. In one embodiment,the elevator architecture shown in FIG. 1 may need to be changed from aforward and reverse architecture to a pipelined architecture to supportmore than one buffer carrier per elevator assembly.

FIG. 4 illustrates an alternate slot-based system where trolleys areused to transport the TIBs, BIBs, or carriers between the pick and placehandler and the tester racks in accordance with embodiments of thepresent invention. An alternate slot-based system comprises asemi-automated system with a handler 402, elevator 404 and trolley 406combination as a centralized loading/unloading pick-and-place (PnP)station that services multiple testing stations (e.g., station 410)comprised of trolley 416, elevator 418 and slot 420 combinations.Operators or robots are used to move the trolleys of loaded carriersbetween the centralized PnP station 450 and the test stations (e.g.,test station 410). This is used when test times are long, allowing asingle PnP to service more than 1-2 test racks with minimal impact ontest throughput. In this case, the optimal UPH definitely requires theuse of buffer BIBs, TIBs, or carriers, as well as buffer trolleys, tomaximize UPH. Using carriers (with no sockets/electronics) as opposed toBIBs/TIBs with sockets is a definite advantage for this scenario due tothe significantly lower cost of the carriers.

FIG. 5 illustrates the manner in which the socket, the carrier, and thesocket cover combine to form the per-DUT shielding in accordance withembodiments of the present invention. In one embodiment, the DUT 511 islatched into place in a floating configuration 507 within the carrierbase frame 513. The carrier base frame 513 holds the individual floatingper DUT carrier elements. That carrier base frame 513 comprises a metalcomponent 562 and a resin component 561, which holds the DUT 511 inplace. The floating configuration ensures compliance in the x, y, and zdirection. The DUTs on the carrier are situated in respective pockets ofthe carrier on a thin membrane 550.

The embodiment of FIG. 5 may comprise a plunger 508 with an integratedsocket cover. The DUTs (e.g., device 511) rest on the membrane and thesolder balls of the DUTs push through the membrane 550 and make contactwith the socket 510 when the plunger 508 pushes down on the DUT 511. Inother words, the plunger 508 pushes the DUT 511 into the socket 510 andapplies force, so that the solder balls make electrical contact with thesocket 510.

In one embodiment, the per-DUT RF shields are formed though the novelcombination of a plurality of socket covers, a carrier containing aplurality of floating per-DUT carrier elements, and a plurality ofsockets. The floating design of the per-DUT carrier elements providesboth mechanical compliance to compensate for tolerance variations acrossthe full structures of the TIBs that are housed in the test slots, aswell as electrical isolation between the per-DUT carrier elements. Afterthe carrier is inserted into the test slot, the socket covers areactuated, resulting in the compression of the per-DUT cover, carrierelement, and socket. A flange or similar mechanically compliant andelectrically conductive means is used on the top and bottom of thecarrier elements to provide hermetic seals between the layers of eachsandwich of the per-DUT cover, carrier element, and socket. The socketcovers and sockets have already been designed to provide electricalshielding on the top and bottom, respectively, so the hermeticallysealed sandwich provides the required per-DUT electrical isolation.

Note that embodiments of the present invention use a per-DUT forcecancellation approach where the force of each plunger mechanism iscancelled directly with its accompanying socket. In classical memoryhandlers, the sockets are mounted directly on an extremely rigidsubstrate. While there are typically individual plungers that providethe force that ensures proper contact between the DUT and socket, thisforce is not cancelled on a per-DUT basis, but instead the full force ofall the plungers is cancelled at the level of the entire multi-DUTsocket substrate with the entire multi-plunger assembly. This hasmultiple drawbacks for a high volume system-level test system. In orderto provide the necessary test circuitry that accompanies each socket onthe TIB, a daughter card architecture is often required where circuitryis stacked on multiple cards that are typically fairly thin (where eachdaughter card stack may, e.g., support one socket). If force is canceledat the level of the entire substrate structure instead of on aper-socket basis, these boards would not be able to withstand thesignificant compression force required to ensure proper contact. Alsofor a large TIB with many sockets, even small tolerance variationsacross the TIB can make it difficult to control the forces uniformlyacross the entire structure when cancelling forces at the level of theentire structure.

In order to address these issues, embodiments of the present inventionuse a per-DUT force cancellation approach where the force of eachplunger mechanism (or actuator mechanism) is cancelled directly with itsaccompanying socket. For example, the plunger 508 can be outfitted witha mechanism that latches onto wings that are built into the socket. Notethat when designing the carrier structure, the need to reach through thecarrier at each DUT location to access (e.g., grab) the socket needs tobe addressed.

FIG. 6 illustrates a single site exploded view of a DUT in a carrierwhere socket grippers are used for local force cancellation inaccordance with embodiments of the present invention. As shown the DUTcarrier 608 contains the DUT that is brought into connection with asocket 609 affixed to SIB 610 using a socket actuator 602. The socketactuator 602 in conjunction with the socket grippers 607 providesper-DUT force cancellation.

FIG. 7 depicts a flowchart of an exemplary process of testing DUTsaccording to an embodiment of the present invention. The embodiments ofthe invention, however, are not limited to the description provided byflowchart 600. Rather, it will be apparent to persons skilled in therelevant art(s) from the teachings provided herein that other functionalflows are within the scope and spirit of the present invention.

At block 702, an array of DUTs is disposed on a carrier using a handlerand movement system.

At block 704, the carrier is inserted into a slot of a tester rackassociated with a tester, wherein the tester comprises a plurality ofracks, and wherein each rack comprises a plurality of slots. In oneembodiment, the slots are stacked vertically. In a different embodiment,the slots may also be arranged horizontally.

At block 706, a tester interface board (TIB) is affixed in the slot ofthe tester rack. In one embodiment, the TIB comprises a plurality ofsockets, wherein each socket is operable to receive a device under test(DUT), and wherein each DUT in the array of DUTs aligns with arespective socket on the tester interface board.

At block 708, a socket cover above each DUT is actuated in order to pushthe respective DUT down to make contact with a respective socket.

At step 710, each DUT in the array of DUTs is tested.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the invention to the precise forms disclosed. Many modificationsand variations are possible in view of the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with various modifications as may be suited to theparticular use contemplated.

What is claimed is:
 1. A testing apparatus comprising: a testercomprising a plurality of racks, wherein each rack comprises a pluralityof slots, wherein each slot comprises: an interface board affixed in aslot of a rack, wherein the interface board comprises test circuitry anda plurality of sockets, each socket of the plurality of sockets operableto receive a device under test (DUT); and a carrier comprising an arrayof DUTs, wherein the carrier is operable to position into the slot ofthe rack, and wherein each DUT in the array of DUTs aligns with arespective socket of the plurality of sockets on the interface board; apick-and-place mechanism for loading the array of DUTs into the carrier;and an elevator for transporting the carrier to the slot of the rack. 2.The testing apparatus of claim 1, wherein the plurality of slots arevertically oriented.
 3. The testing apparatus of claim 1, wherein theplurality of slots are horizontally oriented.
 4. The testing apparatusof claim 1, wherein each slot of the plurality of slots furthercomprises a plurality of socket covers, wherein each socket cover of theplurality of socket covers is operable to actuate a top portion of arespective DUT of the array of DUTs in the carrier.
 5. The testingapparatus of claim 1, wherein the array of DUTs comprise RF devices. 6.The testing apparatus of claim 1, wherein each slot of the plurality ofslots further comprises a plurality of socket covers, wherein eachsocket cover of the plurality of socket covers is operable to actuate atop portion of a respective DUT of the array of DUTs in the carrier, andwherein the carrier is disposed between the interface board and theplurality of socket covers.
 7. The testing apparatus of claim 1, whereinthe elevator comprises a dual-slot elevator, wherein the dual-slotelevator further comprises two slots, wherein a first slot is operableto transport the carrier to the slot of the rack, and wherein a secondslot is operable to transport a different carrier previously loaded intothe slot of the rack.
 8. A method of testing DUTs comprising: disposingan array of DUTs on a carrier using a pick-and-place mechanism;transporting the carrier to a slot of a rack associated with a testerusing an elevator, wherein the tester comprises a plurality of racks,wherein each rack of the plurality of racks comprises a plurality ofslots; inserting the carrier into the slot of the rack; affixing aninterface board in the slot of the rack, wherein the interface boardcomprises a plurality of sockets, and wherein each socket of theplurality of sockets is operable to receive a respective device undertest (DUT), and wherein each DUT in the array of DUTs aligns with arespective socket of the plurality of sockets on the interface board;and actuating a socket cover of a plurality of socket covers onto eachDUT in the array of DUTs to push the respective DUT to make physical andelectrical contact with a respective socket of the plurality of sockets.9. The method of claim 8, wherein each respective socket of theplurality of sockets, the carrier and an associated respective socketcover of the plurality of socket covers together form an electricalshield around an associated DUT.
 10. The method of claim 8, wherein theplurality of slots are vertically oriented.
 11. The method of claim 8,wherein the plurality of slots are horizontally oriented.
 12. The methodof claim 8, wherein the elevator comprises a dual-slot elevator, whereinthe dual-slot elevator comprises two slots, wherein a first slot isoperable to transport the carrier to the slot of the rack, and wherein asecond slot is operable to transport a different carrier previouslyloaded into the slot of the rack.
 13. The method of claim 8, wherein theactuating is performed by a socket actuator, and wherein the actuatingcomprises latching the socket actuator onto a socket gripper associatedwith each socket of the plurality of sockets to provide per-DUT forcecancellation.
 14. A testing system comprising: a station operable toload and unload devices under test (DUTs) from a plurality of carriers,wherein the station comprises a pick-and-place mechanism and a trolleyoperable to transport the plurality of carriers between the station andat least one tester; and the at least one tester comprising a pluralityof racks, wherein each rack comprises a plurality of slots, wherein eachslot comprises: an interface board affixed in a slot of a rack, whereinthe interface board comprises test circuitry and a plurality of sockets,each socket operable to receive a device under test (DUT); and a carriercomprising an array of DUTs, wherein the carrier is operable to positioninto the slot of the rack, and wherein each DUT in the array of DUTsaligns with a respective socket of the plurality of sockets on theinterface board; and an elevator for transporting the carrier to theslot of the rack from the trolley.
 15. The testing system of claim 14,wherein each respective socket of the plurality of sockets, the carrierand an associated respective socket cover of a plurality of socketcovers together form an electrical shield around an associated DUT. 16.The testing system of claim 15, wherein the station further comprises aplurality of slots for holding the plurality of carriers.
 17. Thetesting system of claim 15, wherein the plurality of slots associatedwith the at least one tester are vertically oriented.
 18. The testingsystem of claim 15, wherein the plurality of slots associated with theat least one tester are horizontally oriented.
 19. The testing system ofclaim 15, wherein each slot of the plurality of slots further comprisesa plurality of socket covers, wherein each socket cover of the pluralityof socket covers is operable to actuate a top portion of a respectiveDUT of the array of DUTs in the carrier.
 20. The testing system of claim15, wherein the elevator comprises a dual-slot elevator, wherein thedual-slot elevator further comprises two slots, wherein a first slot isoperable to transport the carrier to the slot of the rack, and wherein asecond slot is operable to transport a different carrier previouslyloaded into the slot of the rack.